Hydrophobic groups paraffins

In RP-TLC, silica gel plates impregnated with a strong hydrophobic agent (paraffin oil or silicone oil, usually 5%) have been extensively used in the past as nonpolar stationary phases. Nowadays, plates covered with octa-decyl-silanized (ODS) silica gel are available. In this material, the silanol groups are etherified with alkyls containing 8 (Cg) or 18 (Cig) carbon atoms. The low wettability of HPTLC plates coated with highly etherified silica gel poses limitations in the water content of the mobile phase. This problem is circumvented by the use of RP-Cig plates with 50% etherification. However, the presence of free silanol groups may lead to undesirable silanophilic interactions, especially with low water content in the mobile phase. 

Another important member of the liquid crystal family is the solution of amphiphilic molecules. The amphiphilic molecules are tadpole-like. A polar, hydrophilic group is at one end of the amphiphilic molecule while a nonpolar, hydrophobic group is at the other end. Two examples are shown in Figure 1.3. Soap in solution, for example, is a liquid crystal. One end of this molecule, -COO-Na+ is a polar group and is soluble in water, while the other end is a hydrocarbon paraffin group CH3(CH2)i4, dissolved in water. 

When disperse phase of the coarse emulsion wets the membrane wall and suitable surfactants are dissolved in both liquid phases, the process results in a phase inversion namely a coarse OAV emulsion is inverted into a fine W/O emulsion (Figure 6.1c), and vice versa (Suzuki et al, 1999). The main advantage of this method is that a fine emulsion can be easily prepared from a low concentration coarse emulsion at high rates. For polytetrafluoroethylene (PTFE) membrane filters with a mean pore size of 1 im, the maximum dispersed phase volume fraction in phase-inverted emulsions was 0.9 and 0.84 for O/W and W/O emulsions, respectively (Suzuki et al., 1999). Flow-induced phase-inversion (FIPI) phenomenon was observed earlier by Akay (1998) who used a multiple expansion-contraction static mixer (MECSM) consisting of a series of short capillaries with flow dividers. Hino et al. (2000) and Kawashima et al. (1991) inverted a W/O/W emulsion made up of liquid paraffin. Span 80 (a hydrophobic surfactant), and Tween 20 (a hydrophilic surfactant) into a W/ O emulsion by extrusion through polycarbonate membranes with a mean pore sizes of 3 and 8 im. Inside the membrane pores, surfactant molecules are oriented with their hydrophobic groups toward the wall surface and with hydro-phihc groups toward the solubilized water molecules as a result of a lamellar structure formed inside the pores. The structure ruptured at the pore outlets. 

Anionic, in which the surface-active properties are provided by a negatively charged ion a hydrophobic group (e.g., paraffinic chains) is balanced by a negatively charged hydrophilic group (e.g., carboxyl). 

The most useful characteristic of the micelle arises from its inner (alkyl chain) part (Figure 3.17). The inner part consists of alkyl groups that are closely packed. It is known that these clusters behave as liquid paraffin (Cn H2n+2). The alkyl chains are thus not fully extended. Hence, one would expect that this inner hydrophobic part of the micelle should exhibit properties that are common to alkanes, such as ability to solubilize all kinds of water-insoluble organic compounds. The solute enters the alkyl core of the micelle and it swells. Equilibrium is reached when the ratio between moles soluteimoles detergent is reached corresponding to the thermodynamic value. 

Examples of common hydrophobes include alkylphenol, fatty alcohol, paraffin, olefins, and alkylbenzene. Examples of common hydrophiles include ethylene oxide (EO), sulfates, sulfonates, phosphates, and carboxylic acid groups. Depending on the charged nature of the head group, surfactants are classified as ... 

Most softeners consist of molecules with both a hydrophobic and a hydrophilic part. Therefore, they can be classified as surfactants (surface active agents) and are to be found concentrated at the fibre surfaces. Most softeners have a low water solubility. Therefore softening products are usually sold as oil in water emulsions containing 20-30 % solids. The softener molecules typically contain a long alkyl group, sometimes branched, of more than 16 and up to 22 carbon atoms, but most have 18 corresponding to the stearyl residue. Exceptions to this molecular structure are the special categories of silicones, paraffins and polyethylene softeners. About one-third of the softeners used in the textile industry are silicone based. 

The best activity was observed for PCMEDDAC dissolved in n-hexane. Initial waxy crude oil behaves hke a viscoplastic fluid. Doped by PCMEDDAC, waxy oil approaches a Newtonian liquid, and the shear stress decreases considerably due to the modification of the paraffin crystals by the hydropho-bized macromolecules, hi oily environments, PCMEDDAC forms micelles consisting of a hydrophihc core (made of the betaine groups) and a hydrophobic corona (made of the dodecyl groups). The PPD mechanism of PCMEDDAC with respect to waxy crude oil suggests the adsorption of definite fractions of paraffin molecules on the surface of micelles and further retardation of agglomeration. 

One of the methods of protecting explosives against moisture consists in using a hydrophobic envelope, such as paper impregnated with hydrophobic sub stances more efficient than paraffin, such as paraffin with added substances containing polar groups — pitch, asphalt, petroleum tar etc. or using a polyethylene envelope. 

The paraffin chain radical is hydrophobic and the solubility of the alcohol is merely due to the hydrophilic OH-groups. It is known, that the surface tension reduction by organic substances decreases with increasing chain... 

Because of its nonpolar and hydrophobic character, the mercury-water may serve as a good model interface for the adsorption study and determination of the organic substances that are adsorbed primarily because of hydrophobic expulsion. There is generally a proportionality of adsorbability (free energy of adsorption) found at the mercury electrode to a number of -CH2 groups in paraffinic hydrocarbon residues in nonpolar surfactants and a similar relation between the octanol water partition coefficient and chain length. This was recently also illustrated in the case of adsorption of aliphatic fatty acids (Ulrich ct al., 1988). 

Fig. 14. Schematic depiction of selected physical and chemical events during fat digestion. The 1- and 3-ester linkages of triglyceride (upper left) are cleaved by lipase, forming 2-monoglyceride and fatty acid. These lipolytic products leave the oil-water interface and are dispersed in the aqueous phase as mixed bile acids-lipolytic product micelles. A proposed molecular arrangement of the bile acid-lipolytic product micelle is shown in cross-section this model is based on studies of the bile acid-lecithin micelle (65). In this model, the hydrophobic back of the bile acid molecule apposes the paraffinic chains of the lipolytic products, and the hydroxy groups of the bile acid molecule are toward the aqueous phase. The paraffin chains of the interior of the micelle are liquid, thus permitting other water-insoluble molecules such as cholesterol and fat-soluble vitamins to dissolve in the micelle. Indeed, the solvent capacity of the bile acid-lipolytic product micelle is contributed chiefly by the paraffin chains of the lipolytic products.

Puskas et al. extracted paraffinic deposits from oil wells and pipelines (47). This hydrophobic paraffin derivative had a high molar mass and melting point and contained polar end groups (carbonyls). This paraffinic derivative stabilized water-in-oil emulsions at concentrations of 1 to 2%. 

The solutions of amphiphilic molecules form another class of the LC family. The amphiphiles are hydrophilic/hydrophobic molecules. One end of the molecule consists of a polar hydrophilic group and the other end is formed by a nonpolar hydrophobic tail. Soap forms a LC phase in solution. In Figure 6, sodium laureate is shown as an example for an amphiphile, -COO -Na+ is the polar group and soluble in water whereas the hydrocarbon paraffin group, CHj(CH2)j4 -, is hydrophobic. 

It contains a linear paraffin chain containing 12 carbon atoms, which is hydrophobic (dodecane is insoluble in water) and lipophilic (meaning that it has an affinity for fats). It also has an SOjNa group which is strongly hydrophilic, being ionisable. 

Hydrophobic properties are achieved by the application of the water/oU repellent treatment to the substrates (Bahners et al., 2008). The main product groups for this treatment are (1) metal salt paraffin dispersion, (2) polysUoxane and (3) fluorocarbon polymers. The surface of the substrates must be covered with molecules in such a way that their hydrophobic radicals are ideally positioned as parallel as possible, facing outwards, during the chemical finishing with these products. 

Metal salt paraffin dispersions (such as aluminium) are products positively charged due to the trivalent aluminium salt, which produces a counter-polar charge on the fibre surface. Polysiloxanes form a fibre-encircling silicone film with methyl groups perpendicular to the siuface. The hydrophobicity of the finish is affected by the film formation... 

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